1. Field of the Invention The present invention is directed to a remotely controllable circuit breaker, and more particularly to such a circuit breaker having, in addition to a manual handle for closing and opening a breaker contact, an electromagnet which responds to a remote signal for closing and opening the breaker contact.
2. Description of the Prior Art
Remotely controllable circuit breakers have been extensively utilized for load managements. One such prior breaker of general type is proposed in U.S. Pat. No. 4,529,951 in which a manual handle for opening and closing a breaker contact is directly connected to an electromagnet to be controlled thereby. Although such two-way control allows the breaker contact to be controlled for managing a load either by a remote control signal supplied to energize the electromagnet from a remote station or by a direct manipulation of the handle, it poses a potential hazard that the load may be turned on by the operation at the remote station while it is not desired at the locale station near the breaker, or the vice versa. This unintentional energization of the load should be avoided particularly when a heavy duty power load is managed for ensuring safe working environment. To overcome the above disadvantage, a breaker is demanded to have a remote control capability which can allow the breaker contact to be controlled under a desired combination of the handle and remote control operations. A contactor device disclosed in U.S. Pat. No. 4,473,860 gives a solution to the above problem, although it is not so intended. The device, in which the closing and opening of a main contact is also controlled by an electromagnet receiving a remote signal, includes a control switch which is actuated by a reset handle to be closed and opened independently of the electromagnet operation. The control switch is connected in a control circuit in series relation with the electromagnet so that the main contact can be closed only when the control switch is closed and the electromagnet is energized by a remote control signal. The device also includes an overcurrent responsive tripping mechanism which is interposed between the handle and the control switch and is released or unlatched upon a predetermined fault current condition to open the control switch and in turn deenergize the electromagnet for circuit interruption. The control switch is kept opened by the tripping mechanism until the handle is manipulated to reset the tripping mechanism. In this device, the tripped circuit interruption is made only through the deactivation of the electromagnet. In other words, the fault current responsive tripping of the main contact involves the operations of the tripping mechanism linked to the handle, the control switch, and the electromagnet. Thus, the prior device requires a complicated structure or operational linkage between a fault current sensor and the main contact, which may lower the reliability of the tripped circuit interruption. In addition to the above disadvantage, this device is further found to be inconvenient when the handle is utilized to manipulate the main contact, since the handle is interlocked with the tripping mechanism and always drags the same as the handle is manipulated between its ON-position and OFF-position. The interposition of the tripping mechanism between the handle and the control circuit is therefore likely to interfere with simple and reliable handle structure and movement.